Unusual location and characterization of Cu/Zn-containing superoxide dismutase from filamentous fungus Humicola lutea

Effect of CeO2, TiO2 and SiO2 nanoparticles on the growth and quality of model medicinal plant Salvia miltiorrhiza by acting on soil microenvironment

In this study, a six-month pot experiment was conducted to explore the effects of nanoparticles (NPs), including CeO2, TiO2 and SiO2 NPs at 200 and 800 mg/kg, on the growth and quality of model medicinal plant Salvia miltiorrhiza. A control group was implemented without the application of NPs. Results showed that NPs had no significant effect on root biomass. Treatment with 200 mg/kg of SiO2 NPs significantly increased the total tanshinone content by 44.07 %, while 200 mg/kg of CeO2 NPs were conducive to a 22.34 % increase in salvianolic acid B content. Exposure to CeO2 NPs induced a substantial rise in the MDA content in leaves (176.25 % and 329.15 % under low and high concentration exposure, respectively), resulting in pronounced oxidative stress. However, TiO2 and SiO2 NPs did not evoke a robust response from the antioxidant system. Besides, high doses of CeO2 NP-amended soil led to reduced nitrogen, phosphorus and potassium contents. Furthermore, the NP amendment disturbed the carbon and nitrogen metabolism in the plant rhizosphere and reshaped the rhizosphere microbial community structure. The application of CeO2 and TiO2 NPs promoted the accumulation of metabolites with antioxidant functions, such as D-altrose, trehalose, arachidonic acid and ergosterol. NPs displayed a notable suppressive effect on pathogenic fungi (Fusarium and Gibberella) in the rhizosphere, while enriching beneficial taxa with disease resistance, heavy metal antagonism and plant growth promotion ability (Lysobacter, Streptomycetaceae, Bacillaceae and Hannaella). Correlation analysis indicated the involvement of rhizosphere microorganisms in plant adaptation to NP amendments. NPs regulate plant growth and quality by altering soil properties, rhizosphere microbial community structure, and influencing plant and rhizosphere microbe metabolism. These findings were beneficial to deepening the understanding of the mechanism by which NPs affect medicinal plants.

CuO, ZnO, and γ-Fe2O3 nanoparticles modified the underground biomass and rhizosphere microbial community of Salvia miltiorrhiza (Bge.) after 165-day exposure

To investigate whether metal oxide nanoparticles exhibit toxicity or positive effects on medicinal plants, CuO, ZnO, and γ-Fe₂O₃ nanoparticles (NPs), at concentrations of 100 and 700 mg kg^-1_, were introduced into the cultivation of Salvia miltiorrhiza (Bge.). Metal elemental contents, chemical constituents, biomass and the structure of the rhizosphere microbial community was used to estimate this effect. The results indicated CuO NPs increased the Cu content and ZnO NPs increased the Zn content significantly as exposure increased, γ-Fe₂O₃ NPs had no significant effect on Fe content in S. miltiorrhiza roots, while 100 mg kg^-1 ZnO and CuO NPs significantly decreased the Fe content in roots. Additionally, ZnO and γ-Fe₂O₃ NPs increased the underground biomass, and diameter of S. miltiorrhiza roots. However, these three metal oxide nanoparticles had no significant effect on total tanshinones, while the 700 mg kg^-1 γ-Fe₂O₃ NPs treatment increased salvianolic acid B content by 36.46%. High-throughput sequencing indicated at 700 mg kg^-1 ZnO NPs, the relative abundance of Humicola (Zn superoxide dismutase producer), was notably increased by 97.46%, and that of Arenimonas, Thiobacillus and Methylobacillus (taxa related to heavy metal tolerance) was significantly increased by 297.14%, 220.26% and 107.00%. The 700 mg kg^-1 CuO NPs exposure caused a significant increase in the relative abundances of Sphingomonas (a copper-resistant and N₂-fixing genus) and Flavisolibacter (stripe rust biocontrol bacteria) by 127.32% and 118.33%. To our best knowledge, this is the first study to examine the potential impact of NPs on the growth and rhizosphere microorganisms of S. miltiorrhiza.

A Preliminary Investigation on Metal Bioaccumulation by Perenniporia fraxinea

The lignicolous macrofungus Perenniporia fraxinea has drawn increased attention due to its role as a pathogen of ornamentals in urban sites. The present study investigated the bioaccumulation of heavy metals by P. fraxinea. Sporophores were collected from urban and suburban areas in Pavia (Northern Italy) and analyzed for metals content (Cd, Hg, Pb, Ni, Cr, Cu, Fe, Mn, Zn) by inductively coupled plasma mass spectrometer and inductively coupled plasma optical emission spectroscopy, after microwave acidic digestion. On the basis of the obtained results the potential bioaccumulation capability of P. fraxinea was investigated. The isolates were grown in a culture medium enriched with different concentrations of Cd and Hg, chosen as probes of environmental pollution, and Cu for comparison. As P. fraxinea grows in the presence of Cd, Hg and Cu, it seems to be a potential tool in environmental monitoring.

Copper stress and filamentous fungus Humicola lutea 103 — ultrastructural changes and activities of key metabolic enzymes

Humicola lutea 103 is a copper-tolerant fungal strain able to grow in the presence of 300 μg·mL–1 Cu2+ under submerged cultivation. To prevent the consequences of copper overload, microorganisms have evolved molecular mechanisms that regulate its uptake, intracellular traffic, storage, and efflux. In spite of this avoidance strategy, high heavy-metal concentrations caused distinct and widespread ultrastructural alterations in H. lutea. The mitochondria were the first and main target of the toxic action. The effect of copper on activities of the key enzymes (hexokinase, glucose-6-phosphate dehydrogenase, malate dehydrogenase, and isocitrate dehydrogenase) included in the 3 main metabolic pathways, glycolysis, pentose phosphate pathway, and tricarboxylic acid cycle, was investigated. High metal concentrations exhibited a dramatic negative effect on hexokinase, while the other 3 enzymes showed a significant and dose-dependent stimulation. On the basis of the present and previous results we concluded that the copper-induced oxidative stress plays an important role in the fungal tolerance to high Cu 2+ concentrations.

Structural analysis and molecular modelling of the Cu/Zn-SOD from fungal strain Humicola lutea 103

The native form of Cu/Zn-superoxide dismutase, isolated from fungal strain Humicola lutea 103 is a homodimer that coordinates one Cu(2+) and one Zn(2+) per monomer. Cu(2+) and Zn(2+) ions play crucial roles in enzyme activity and structural stability, respectively. It was established that HLSOD shows high pH and temperature stability. Thermostability of the glycosylated enzyme Cu/Zn-SOD, isolated from fungal strain H. lutea 103, was determined by CD spectroscopy. Determination of reversibility toward thermal denaturation for HLSOD allowed several thermodynamic parameters to be calculated. In this communication we report the conditions under which reversible denaturation of HLSOD exists. The narrow range over which the system is reversible has been determined using the strongest test of two important thermodynamic independent variables (T and pH). Combining both these variables, the "phase diagram" was determined, as a result of which the real thermodynamic parameters (ΔC(p), ΔH(exp)°, and ΔG(exp)°) was established. Because very narrow pH-interval of transitions we assume they are as result of overlapping of two simple transitions. It was found that ΔH(o) is independent from pH with a value of 1.3 kcal/mol and 2.8 kcal/mol for the first and the second transition, respectively. ΔG(o) was pH-dependent in all studied pH-interval. This means that the transitions are entropically driven, these. Based on this, these processes can be described as hydrophobic rearrangement of the quaternary structure. It was also found that glycosylation does not influence the stability of the enzyme because the carbohydrate chain is exposed on the surface of the molecule.

Oxidative stress in industrial fungi

Fungi are amongst the most industrially important microorganisms in current use within the biotechnology industry. Most such fungal cultures are highly aerobic in nature, a character that has been frequently referred to in both reactor design and fungal physiology. The most fundamentally significant outcome of the highly aerobic growth environment in fermenter vessels is the need for the fungal culture to effectively combat in the intracellular environment the negative consequences of high oxygen transfer rates. The use of oxygen as the respiratory substrate is frequently reported to lead to the development of oxidative stress, mainly due to oxygen-derived free radicals, which are collectively termed as reactive oxygen species (ROS). Recently, there has been extensive research on the occurrence, extent, and consequences of oxidative stress in microorganisms, and the underlying mechanisms through which cells prevent and repair the damage caused by ROS. In the present study, we critically review the current understanding of oxidative stress events in industrially relevant fungi. The review first describes the current state of knowledge of ROS concisely, and then the various antioxidant strategies employed by fungal cells to counteract the deleterious effects, together with their implications in fungal bioprocessing are also discussed. Finally, some recommendations for further research are made.